Wireless transmission of data and power has emerged as a popular and essential characteristic of implantable medical devices such as cardiac pacemakers, implantable cardioverter defibrillators, recording devices, neuromuscular stimulators, prosthetic devices such as cochlear implants. Inductive coupling is popular and effective means to realize transcutaneous link for implanted biomedical devices because a coil pair may be used both for data as well as power transmission to the implanted circuitry.
Implantable prosthesis devices are generally required to be small to reduce the trauma and other complications arising from the implantation and maintenance of foreign matter inside a patient's body. For example, a cochlear implant typically include an external component and an internal component. The external component is external to the patient's body whereas the internal component is implanted in the patient's body.
The external component includes a microphone for sensing ambient sounds and a signal processor for generating processed electrical signals corresponding to these sounds. The processed electrical signals are transmitted, using a transmitter coil of the external component, to the internal component that applies the same to the auditory nerve of the patient through an array of electrodes. Because the internal component may not have a permanent power supply, power for the component is also derived from the external component. The means for providing both power and communication between the internal and external components is typically a pair of coils, the transmitter coil in the external component and a receiver coil in the internal component. The coils are generally planar and are positioned parallel to each other so that energy is coupled through the skin and flesh of the patient from the transmitter coil to the receiver coil for the purpose of powering and/or controlling the internal component.
FIG. 1A illustrates an electromagnetic coupling in a conventional cochlear implant. The cochlear implant 100 works on the principle of the external component 102 being coupled to an internal component 104 via an electromagnetic inductive coupling 106. The purpose is to activate auditory nerve 126 by using an electrode array placed in cochlea 124, thus allowing profoundly deaf patients (i.e., those whose middle and/or outer ear is dysfunctional, but whose auditory nerve remains intact) to hear again.
Referring now to FIG. 1B that illustrates a schematic diagram of the external component 102 and the internal component 104 in the conventional cochlear implant. The external component 102 includes a microphone or a multi-microphone assembly 110, a signal processor 112, an energy source 114 and a transmitter coil 116. The microphone or multi-microphone assembly 102 picks up an audio sound 108 from patient's environment and converts the audio sound into electrical signals. The signal processor 112 processes the electrical signals to generate the processed electrical signals, typically a sequence of pulses of varying width and/or amplitude. The processed electrical signals, once generated, are transmitted to a stimulation electronics 120 of the internal component 104 via the inductive link 106 established between the transmitter coil 116 and a receiver coil 118. The stimulation electronics 120, in response to receipt of the processed electrical signals, generates appropriate pulses of stimulating electrical signals that are applied to one or more electrodes of an electrode array 122 that is inserted into the cochlea 124 of the patient. It is the stimulating electrical signals that directly stimulate the auditory nerve 126 and provides the patient with the sensation of hearing.
FIG. 1C shows the internal arrangement of elements in the internal component in a partial cross section view of a conventional cochlear implant. The internal component 104 includes an implantable hermetical housing 128. The implantable hermetic housing 128 includes the stimulation electronics 120, the receiver coil 118 and a magnet 130 for the external antenna holding. The magnet 130 is used to hold and align the receiver coil 118 with the transmitter coil (FIG. 1 B, 116) of the external component (FIG. 1 B, 102) directly over the location where the receiver coil 118 associated with the implanted stimulation electronics 120 is located. Typically, the housing includes a ceramic body 136 hermetically closed with a flat titanium cover 132. The housing further includes feedthroughs 134. The feedthroughs 134 provide an electrically conducting path extending from interior of a hermetically sealed housing, to an external location outside the housing. This arrangement allows one or more electrical connections to be made between the electrode array (FIG. 1 B, 122) and the stimulation electronics (FIG. 1B, 120) within the hermetically sealed housing, whilst protecting the circuitry or other hermetically sealed elements from any damage or malfunction that may result from exposure to the environment surrounding the housing.
Placing the receiver coil 118 with the stimulation electronics 120 inside the hermetic housing is typically preferred because of the material that may be used for the coil. For example an insulated copper wire, considered to be a preferable material for coil, may be used for manufacturing the receiver coil. However, this results in a decrease in distance d between the receiver coil 118 and the metallic component such as titanium cover 132. The metallic component 132 typically is a distal surface from skin of the patient when the housing 128 is in implanted position. This distance d is a major factor for determining performance of the inductive link. When the distance d between the hermetically sealed receiver coil 118 and the metallic components 132 is small, the inductive link performance between the transmitter coil 116 and the receiver coil 118 is poor partly because the receiver coil 118 is further away from the transmitter coil 116. In fact, the proximity of the receiver coil 118 to the metallic component 132 results in undesirable magnetic interferences, negatively affecting the inductive link yield. Therefore, when the distance d decreases, the performance of the inductive link decreases too.
Therefore, there is a need to provide an alternative solution that overcomes the shortcomings of the existing solutions.